Problem:    Various inconsistencies in test files.
Solution:   Add modelines where they were missing.  Use Check commands instead
            of silently skipping over tests.  Adjust indents and comments.
            (Ken Takata, closes #6695)

Problem:    FreeBSD: test for sourcing utf-8 is skipped.
Solution:   Run the matchadd_conceal test separately to avoid that setting
            'term' to "ansi" causes problems for other tests. (Ozaki Kiichi,
            closes #5721)

Problem:    Tests fail on Cirrus CI for FreeBSD.
Solution:   Fix a test and skip some. (Christian Brabandt, closes #5281)

Problem:    Too many #ifdefs.
Solution:   Graduate FEAT_MBYTE, the final chapter.

Problem:    Still too many old style tests.
Solution:   Convert a few more tests to new style. (Yegappan Lakshmanan,
            closes #2256)

Problem:    Buffer overflow when using latin1 character with feedkeys().
Solution:   Check for an illegal character.  Add a test.